This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
A Brayton cycle engine commonly known as a gas turbine engine often has a turbine compressor that is mechanically linked to an expander turbine through a shaft. The turbine compressor can be used to compress a flow of air ingested by the turbine compressor. The compressed air is then flowed to a combustor. In the combustor, fuel is injected and ignited to create a continuous flame. The high pressure exhaust gases from the flame are flowed into the expander turbine, which generates mechanical energy from the exhaust gas as it expands. Such a gas turbine engine can be adapted to combust fuel at near stoichiometric conditions with exhaust gas recirculation (EGR) and may be referred to as an ultra-low emissions technology (ULET) engine.
The exhaust gas may include a mixture of nitrogen, carbon dioxide, water, and any number of other gaseous components. A portion of the exhaust gas may be extracted from the engine or EGR system and, following some treatment, may be injected into a reservoir for pressure maintenance or enhanced hydrocarbon recovery from a subterranean reservoir or for carbon sequestration. For some applications, at least a portion of the nitrogen product from the extracted exhaust gas is not used for reservoir pressure maintenance or enhanced hydrocarbon recovery. Therefore, at least a portion of the nitrogen product may be vented to the atmosphere after expansion and power recovery. For some current applications, the excess nitrogen product is used in conjunction with a high temperature expansion process to increase the amount of power recovered from the system. However, the excess nitrogen product may also be used for a variety of other purposes.
U.S. Pat. No. 4,271,664 to Earnest discloses a turbine engine with exhaust gas recirculation. The engine has a main power turbine operating on an open-loop Brayton cycle. The air supply to the main power turbine is furnished by a compressor independently driven by the turbine of a closed-loop Rankine cycle which derives heat energy from the exhaust of the Brayton turbine. A portion of the exhaust gas is recirculated into the compressor inlet during part-load operation. However, no additional uses are disclosed for the recycled exhaust.
U.S. Pat. No. 6,412,302 to Foglietta et al. describes a process for producing a liquefied natural gas stream. The process includes cooling at least a portion of a pressurized natural gas feed stream by heat exchange contact with first and second expanded refrigerants that are used in independent refrigeration cycles. The first expanded refrigerant is selected from methane, ethane, and treated and pressurized natural gas, while the second expanded refrigerant is nitrogen. However, generation of the second expanded refrigerant from exhaust gas including nitrogen is not disclosed.